1. Field of the Invention
This invention relates to lasers, and more particularly, it relates to an arrangement for enhancing the starting characteristics of cold cathode gas lasers, particularly in the dark environment of a protective housing.
2. Description of the Prior Art Including Prior Art Statement
A common technique for pumping the laser medium of a cold cathode gas laser involves establishing an electrical discharge between the anode and cathode of the laser tube. Conventionally, such discharges are both initiated and maintained by application of a voltage of sufficient magnitude between the anode and the cathode. The applied voltage first produces breakdown of the laser gas to initiate the discharge, after which the magnitude of the voltage drops to a level sufficient to sustain the discharge at the required current density.
Under certain adverse conditions, however, gas breakdown will not occur in response to an applied voltage, and a discharge will not be initiated. In particular, for a laser tube encapsulated in a protective housing, the tube is in darkness prior to initiation of a discharge therein and is normally at a relatively low temperature, both of these conditions being adverse to gas breakdown. This lowers the reliability with which the laser can be started.
In the past, in order to improve the starting reliability of cold cathode gas lasers, an insulated electrically conductive wire has been provided between the laser tube and the protective housing and extending longitudinally along the laser tube for substantially the length of the tube. One end of the wire was electrically connected to the positive terminal of the laser power supply, with the other end of the wire terminating in a loop extending circumferentially about the laser tube near the adjacent end of the tube. For further details concerning laser starting enhancing arrangements of this type, reference may be made to U.S. Pat. No. 3,792,372, issued Feb. 12, 1974 to John T. Mark. As is further disclosed in this patent, in order to compensate for effects of the capacitance produced by such an external wire, a resistance of a value ranging from 20 megohms to 500 megohms may be inserted in series with the wire.
Although external wire-loop laser starting arrangements of the type described above have achieved some improvement in the starting reliability of cold cathode gas lasers in a dark environment, difficulties are still being experienced. Specifically, different starting voltages are frequently required to start different individual laser tubes built to the same design specifications. Moreover, the time delay between application of the starting voltage and commencement of the discharge also is non-uniform for individual laser tubes.